The exocyst is an octameric protein complex essential for exocytosis. While the exocyst functions to tether secretory vesicles at the plasma membrane for subsequent fusion, most of the exocyst components are localized to internal membrane compartments such as the recycling endosomes. It is thought that members of the exocyst associate with the vesicles when they bud from the recycling endosomes and are delivered to the plasma membrane for vesicle tethering. However, how the exocyst physically associates with the recycling endosomes is unknown. Here I hypothesize that the exocyst directly interacts with the EHD family proteins, which mediate vesicle formation from the endosomes. This interaction links vesicle generation from the donor compartments to subsequent vesicle tethering at the plasma membrane. The exocyst-EHD interaction is regulated by Ral GTPases, which are regulators of membrane trafficking and cell migration downstream of EGF signaling. The exocyst, EHD proteins, and Ral have all previously been implicated in cell migration. I hypothesize that the exocyst- EHD interaction, under the regulation by Ral, is important for the recycling of integrins (a cargo of the recycling endosomes) to the leading edge of cells for directional migration. Biochemical and cell biological experiments will be carried out to examine the interaction of the exocyst with EHD proteins and its regulation by Ral. Furthermore, the functional implication of this interaction in integrin recycling and cell motility will be investigated. This study will not only help elucidate the molecular mechanisms of protein recycling from endosomes, but also shed light to the function of membrane trafficking in cell migration and tumor invasion. PUBLIC HEALTH RELEVANCE: Directional cell migration is fundamental to many physiological processes such as chemotaxis, embryogenesis, and neuronal development. Studying the molecular basis of cell migration will help us understand these physiological processes and shed light on the pathogenesis of diseases such as neurological disorders and cancer.